Siemens 6MD85 Manual page 389

Checking Closing Conditions of Synchronous Systems
[losynsyn_adj_comm, 1, en_US]
Figure 6-76
The frequency difference is very low in the synchronous systems operating mode. It is below the threshold
value f-threshold ASYN<->SYN. The status is signaled via the State f-synchronous indication.
The parameters ΔV and Δα are checked for issuing a closure release (see
sync. conditio. OK signals that both setting values (conditions) are reached. If the conditions remain
fulfilled over the set time delay (parameter Delay close command), the release for closing is issued (see
also chapter 6.4.7.1
Every fulfilled condition is signaled individually via the indications Voltage difference OK and Angle
difference OK .
If a condition is not fulfilled, detailed information on why the condition is not fulfilled is provided via indica-
tions. If, for example, the differential voltage is outside the setting limits, the indication V dif.too
large(V2>V1) is issued. The indication indirectly contains information that the voltage V2 must be
increased for successful synchronization.
If the Expanded delta-f options stage type is configured and the parameter (_:142) Limit dfdiff/dt
for asyn. op is activated, the rate of change of the differential frequency is also checked. If the permissible
frequency change rate (parameter (_:143) Max. value dfdiff/dt asyn) is exceeded, the indication
(_:329) dfdiff/dt too large is generated.
SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017
Closing Conditions when Switching Synchronous Systems
Description).
Control Functions
6.4 Synchronization Function
Figure 6-77). The indication All
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